Kei Sakamoto

How long does the protective effect on eccentric exercise-induced muscle damage last?

PURPOSE One bout of eccentric exercise produces an adaptation that reduces muscle damage in subsequent bouts. Because it is not known how long this adaptation lasts, the present study investigated the maximal length of the attenuated changes in muscle damage indicators after high-force eccentric exercise. METHODS Male students (N = 35) were placed into three groups and performed two bouts of eccentric exercise of the nondominant elbow flexors separated by either 6 (N = 14), 9 (N = 11), or 12 (N = 10) months. Maximal isometric force (MIF), range of motion (ROM), upper arm circumference (CIR), muscle soreness (SOR), and plasma creatine kinase activity (CK) were measured before and for 5 d after exercise. Magnetic resonance (MR) images of the transverse and longitudinal scans of the upper arm were taken 4 d after exercise. Changes in the criterion measures were compared between the first and second bouts and between groups by a two-way repeated measures ANOVA. RESULTS A faster recovery in MIF was evident after a second bout performed at 6 or 9 months, and reduced SOR as well as smaller increases in CIR, CK, and T2 relaxation time of MR images also occurred after the second exercise bout at 6 months compared with initial responses. No significant differences between the bouts were found for ROM, and the 12-month group did not show any repeated bout effect. CONCLUSION These results show that the repeated bout effect for most of the criterion measures lasts at least 6 months but is lost between 9 and 12 months.

Effect of elbow joint angle on the magnitude of muscle damage to the elbow flexors

PURPOSE It has been shown that eccentric actions at a long muscle length result in a larger decrease in force and more muscle tenderness compared with those at a short muscle length. To further investigate the effect of elbow joint angle on the development of muscle damage, this study compared two maximal eccentric exercise regimens in which the starting position of the action was different, but the range of movement was the same. METHODS One arm of 10 male students performed 24 maximal eccentric actions of the elbow flexors at the elbow joint angle from 0.87 to 2.27 rad (50-130 degrees: S condition) and the other arm at the elbow joint angle from 1.74 to 3.14 rad (100-180 degrees: L condition). Maximal isometric force, range of motion, muscle soreness, plasma creatine kinase activity, upper arm circumference, and B-mode ultrasound pictures of the elbow flexors (US) were measured before and for 5 d postexercise in both conditions. Magnetic resonance imaging (MRI) of the transverse scans of the upper arm was taken at 4 d after exercise. RESULTS All measures changed significantly (P < 0.01) after exercise for both conditions; however, significantly (P < 0.01) larger changes in the measures were found in the L condition compared with the S condition. MRI and US displayed that only the brachialis was damaged for the S condition but the biceps brachii was also damaged for the L condition. CONCLUSION The greater development of muscle damage in the L condition compared with the S condition is likely to be associated with the elbow flexors muscles affected by the exercise.

The adaptive response of MyoD family proteins in overloaded, regenerating and denervated rat muscles

Using Western blot analysis, we investigated whether the amount of myogenic regulatory factors differs in slow-type and fast-type muscles. In addition, we examined the adaptive response of myogenic regulatory factor protein in the overloaded rat muscles by the ablation of synergists, in the regenerating muscles following bupivacaine injection and in the denervated muscle. The amount of myogenin protein in the slow-type muscle was markedly greater. In contrast, the proteins MyoD and Myf-5 were selectively accumulated in the fast-type muscles. A gradual down-regulation of MyoD and Myf-5 proteins was detected in the denervated fast-type muscles, but not in the myogenin protein content. A rapid down-regulation of myogenic regulatory factor protein was observed both of the mechanically overloaded and in the regenerating muscles. These results indicate that the fast-type-specific gene expression in muscle is modulated by MyoD and Myf-5 proteins and suggest that myogenin protein plays an important role in the reconstruction of damaged neuromuscular connections.

Differential adaptations of insulin-like growth factor-I, basic fibroblast growth factor, and leukemia inhibitory factor in the plantaris muscle of rats by mechanical overloading: an immunohistochemical study

Abstract We investigated changes in several growth factors in the rat plantaris muscle produced by mechanical overloading by ablation of synergists using immunohistochemistry. At 1 and 3 days post surgery, the insulin-like growth factor-I (IGF-I) level was slightly increased in the cytosol and markedly increased in the invading cells of the extracellular space. Thereafter, the IGF-I immunoreactivity evoked by overloading rapidly decreased to the normal level. The level of leukemia inhibitory factor (LIF), which was not shown to change at 1 day post surgery, was increased in the cytosol at 3, 5, 7 and 10 days and at 2 weeks. Basic fibroblast growth factor (bFGF) immunoreactivity did not change during the entire period of overloading (1 day–3 weeks post surgery). These results indicate that the elevations of the levels of IGF-I and LIF show differential time course in the plantaris muscle subjected to functional overload. Furthermore, bFGF appears not to be related to the compensatory hypertrophy produced by overloading.

The adaptive response of transforming growth factor-β2 and -βRII in the overloaded, regenerating and denervated muscles of rats

Abstract Using a muscle cell line and satellite cell cultures, it has been shown that transforming growth factor-β (TGF-β) has a powerful inhibitory effect on myoblast replication and differentiation. However, little work has been done on the possible role of TGF-β in adult muscle in vivo. Using Western blot and immunohistochemical analyses, we investigated normal distribution of TGF-β2 and TGF-βRII proteins between slow and fast-type muscles, and the adaptive response of these proteins in the mechanically overloaded muscles, in the regenerating muscles following bupivacaine injection and in the denervated muscle after section of sciatic nerve. Slight TGF-β2 immunoreactivity was detected both in slow- and fast-type muscles of mature rat. The amount of TGF-βRII protein was markedly greater in fast-type muscles. In the overloaded muscle, immunohistochemical analysis showed a marked increase in TGF-β2 immunoreactivity in the mononuclear cells (probably endothelial and perithelial or smooth muscle cells of endomysial capillaries) of the extracellular space at 3 and 6 days post surgery. Rapid increase of TGF-β2 protein and concomitant decrease of the receptor (TGF-βRII) were observed in the mechanically overloaded and regenerating muscles. On the other hand, denervation of slow- and fast-type muscles showed a rapid increase in TGF-β2 protein, but did not elicit a concomitant decrease of TGF-βRII. These results indicate that TGF-βRII is preferentially distributed in fast-type muscles. Furthermore, TGF-β2 may play an important role in muscle hypertrophy and regeneration by the usage of TGF-βRII.

Creatine kinase release from regenerated muscles after eccentric contractions in rats.

The purpose of this study was to test the hypothesis that an increase in plasma creatine kinase (CK) activity after eccentric contractions (ECC) would be attenuated in regenerated muscle fibres. Adult male Wistar rats (aged 12–14 weeks) were randomly assigned to a treatment group (n =14) or a control group (n = 10). In the treatment group, 1.2% barium chloride solution (BaCl2) was injected into the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles to induce degeneration and subsequent regeneration. The same amount of isotonic saline solution was injected into TA and EDL for the control group. Histological observation showed that approximately 50% of the fibres in the transverse sections of both muscles underwent necrosis 2 days after BaCl2 injection. The CK activity increased about tenfold at 2–4 h after BaCl2 injection. At 4 weeks after BaCl2 injection, when the regeneration process was almost complete, the TA and EDL of anaesthetized rats from both groups were subjected to ECC in which maximal dorsiflexion was caused by nerve electrical stimulation and the flexed foot was forcibly extended by a lever arm connected to a motor. This action was performed in 2 sets of 30 repetitions. Maximal isometric torque of the dorsiflexors decreased to about 15% (P<0.01) of the pre-ECC value immediately after the exercise. Blood samples were collected before and 2, 4, 12, 24, 48 h after ECC. The CK activity increased significantly (P < 0.01) and peaked at 2–4 h after ECC, and there was no significant difference in the amount of CK increase between the treatment [1007 (SEM 120) IU · I−1] and the control [1064 (SEM 120) IU · 1−1 group. Contrary to the hypothesis, CK release after ECC was not attenuated in muscle regenerated from BaCl2-induced myonecrosis.